Triple citizenship here, although I have a decidedly "neutral" (read: white skin, brown hair) look. Since my "look" doesn't distinguish me in my three countries of citizenship (US, Canada and France), it's my name and accent that baffles people. I don't have an accent when speaking in English (born and raised in the US), but I have a francophone name (Quebecois father and French mother). People don't understand how to pronounce it and wonder where I'm from. I'm from the US. No, no, where we're you born? THE US for F***s sake!
I have an accent when speaking in French simply because I have a mixture of Quebecois and French (my parents). Either way.... to both (Quebecers and French), I'm American, not a REAL Canadian or French. I've lived in Québec for 12 years, been a citizen for 30, but nope, not a real one (even though my name is Quebecois).
It gets fun at the Canada-US border. I'm obliged to show a US passport to come into the States, but then they ask me my status in Canada. Coming back, I have to show my Canadian, but my place of birth shows the US, so they ask me my status there. Basically, no matter where I go, I'm never actually home.
And for god's sake, where did the rumour that I can't have multiple citizenships after the age of 18 arise? Because I get asked that EVERY SINGLE TIME I travel with multiple passports.